1. Field of the Invention
The present invention relates to an eye refractive power measurement apparatus which measures refractive power of an examinee's eye objectively.
2. Description of Related Art
Conventionally, there is known an eye refractive power measurement apparatus comprising a projection optical system for projecting a measurement target onto a fundus of an examinee's eye and a photo-receiving optical system in which a ring-shaped opening is placed in a position conjugate with a pupil of the eye, for photo-receiving reflection light from the fundus as a ring fundus reflection image on a two-dimensional image-pickup element, the apparatus arranged to perform measurement of refractive power of the eye based on a photo-received position of the ring image which is picked up by the two-dimensional image-pickup element.
In addition, an eye refractive power measurement apparatus is disclosed, which has a configuration as described above and is further arranged to display on a monitor a standard deviation as irregular astigmatic power, the standard deviation obtained from differences between refractive power in meridian directions of the eye which is obtained from a ring fundus reflection image subjected to ellipse fitting in order to obtain sphere power, astigmatic power and an astigmatic axial angle of the eye, and refractive power in the meridian directions of the eye which is obtained from an actual fundus reflection image (see Japanese Patent Application Unexamined Publication No. Hei09-276221).
However, when refractive power measurement of an eye of an examinee who has keratoconus that is a kind of irregular astigmatism and analysis of the eye for irregular astigmatism are performed, there is a case where a ring image picked up by the two-dimensional image-pickup element does not greatly differ from that of an examinee's eye which has regular astigmatism. In this case, the eye of the examinee who has keratoconus could be interpreted as a normal eye.